You'd also have to be naive to think that the Nats are anything but lucky to have had their 100 loss seasons coincide with the availability of Strasburg and Harper. Look at the standings in the year before we got Harper, the Mariners were close to passing us on the way to the bottom.
I don't think being as terrible as they were was the plan. I think Kasten and Bowden had the Lerners convinced that they could be respectable on a thin budget, they had their "manager of the future" in Manny Acta and were rebuilding. Being embarrassingly bad was a happy accident.
Sure, I'm happy that we ended up with Strasburg and Harper, but we could have just as easily had a handful more wins each season and ended up with the 2nd or 3rd pick and gotten Dustin Ackley, et al. So, no, the Lerners are not off the hook for my money. I sat through those seasons where the fans seemed to care more than the owners and the owners fielded teams on the cheap. I don't blame Rizzo as much as I put the burden of those missteps on Bowden, the Lerners and Kasten.